The present invention relates to a method of, and apparatus for, removing an insulating coating of a relatively thin electric wire such as a vinyl-coated electric wire, by means of a laser beam without damaging a conductor thereof.
A variety of flat cables have been used popularly nowadays as signal cables for computers, office automation equipment, communication devices or video equipment etc. These flat cables used in these areas usually have a pitch of 1-2 mm, a conductor diameter of about 1 mm, and the number of core wires is between 10 to 60, or more.
Each core wire is made from about seven twisted filaments each having a diameter of one hundred and several tens of microns, usually.
Connection between a flat cable and a conductor is made in various manners.
A typical example is the pin-caulking, in which a specially designed jig is used to connect a flat cable to a predetermined connector. Alternatively, it is possible to remove the coating easily by means of a stripping tool.
Besides, the recent tendency of lighter, thinner, shorter, and smaller products forces electronic parts to be miniaturized and lighter, and the size of printed circuit board is also being made smaller, and still making an improvement of its performance into consideration. On the contrary, the size of flat signal cables connecting printed circuit boards is still not made smaller. An area which is occupied by the connector on the printer circuit board is relatively large and since a gap between stacked printed circuit boards becomes smaller, the flexibility thereof should be higher.
An example of a flat cable which may satisfy the above mentioned requirements comprises 30 thin conductors each composed of seven twisted filaments each having a diameter of 20 microns. The flat cable has a thickness of 500 microns and a width of 15 mm. The flexibility of this cable is superior.
An insulating coating of a conventional flat cable can be removed easily by means of a mechanical stripper since an area of each conductor is as large as about 0.3 mm.sup.2. Further, the pin caulking can be employed therefor with a specially designed jig.
However, for the flat cable as mentioned above whose conductors are very thin, it is almost impossible to use a mechanical stripper for insulating coating removal and the pin caulking can not be applied thereto. In order to avoid this difficulty, a wire stripper 60 as shown in FIG. 1 may be designed, which is a combination of a conventional mechanical stripper and heaters 61a and 61b. In FIG. 1, reference numeral 1 depicts a flat cable.
Since the conductors of such a flat cable are very thin, it is very difficult to bring the edges of the stripper very close to the conductors. Even if this is done, there may be a problem of damage to the conductors since it is necessary to peel the insulating coating off therefrom.
A method of removing an insulating coating of a flat cable by means of a laser beam has been developed to solve these problems.
An example of a conventional apparatus realizing this method is disclosed in Japanese Patent Application Laid-Open No. 25509/1984, which is illustrated FIG. 2 in which shows an electrical wire 1 coated with an insulating material, conductors 2, a fixing jig 40 for clamping the wire 1, a wire clamper 41, a cylinder 42 for driving the clamper 41, a cylinder 43 for driving a fixing jig 44 for fixing the clamper 41, a laser beam generator 50 and a laser beam 51. In operation, the wire 1 is fixed in a predetermined position by the fixing jig 40, and subjected to the laser beam 51 from the laser beam generator 50. The insulating coating of the wire 1 thereby is therefore melted down as shown in FIG. 2a. Thereafter, the wire 1 is transported by the wire fixing jig 40 to a predetermined position in which the clamper 41 is located. In this position, the clamper 41 clamps the wire 1 under a predetermined pressure by the cylinder 42 as shown in FIG. 2b. Then, the clamper fixing jig 44 is moved in a direction, depicted by an arrow in FIG. 2c, by the cylinder 43, so that the insulating coating of the wire 1 is removed, and the conductors 2 are exposed.
In this prior art, there is a problem of cutting the conductors 2 since the wire is irradiated by the laser beams almost without control. Particularly, for a thin flat cable, this problem becomes serious as it is very difficult to control laser beam energy precisely.
Further, in order to form an exposed region of conductors of predetermined size, it is necessary to pull the wire 1 after laser beam irradiation while being clamped by the clamper, and, hence, this requires a mechanism therefor. Further, when the wire 1 is thin, the conductors thereof may be elongated thereby or, in some cases, may be cut.